the Garmin Montana 600.... after a bit of research, it seems like the 600 was designed as a "large screen handheld" (4" diag screen size) to be perfectly compatible with the bluechart software... and waterproof.
the most common version of the montana has land-based map loaded for hiking, driving and geocaching, but the marine version comes pre-loaded with bluechart G2 us offshore/coastal software, but without the land-based maps, I think.
I ordered one to see if it lives up to its claims... so ill give a review after Ive played with it for awhile. I thought about a hardmounted model, but this handheld will lend itself very nicely to the ATV in the off season...
im not sure what the offshore/coastal software includes but according to the outline on the "chart" that is advertised with it, it would include the offshore and coastal waters of entire continental unites states, alaska, hawaii, bahamas and all other lands, water or islands controlled by the united states. Im wondering how much of the navigable river systems it includes... (garmin chart, HXUS039R)